Cold deformation of metals



United States 2,962,401 COLD DEFORMATION OF METALS No Drawing. FiledMar. 17, 1958, Ser. No. 721,702

6 Claims. (Cl. 148-115) The present invention relates to the lubricationof the surface of aluminium during cold forming processes, such as thecold rolling of aluminium (including aluminium alloys) to form sheet orstrip material or in the cutting out or blanking of circles or slugsfrom such material.

In all such processes a lubricant is employed to prevent damage to thesurface finish of the material. It is the present practice in the coldrolling of aluminium to apply a lubricant which comprises a relativelylight petroleum fraction base oil, to which is added a small proportionof a special load-bearing additive.

The additives at present used are generally long chain 3, aliphaticacids, such as lauric acid, and esters of such acids, such as lanolin orbutyl stearate. When the sheet metal ,is annealed after rolling it isfound that its' surface is discoloured by two forms of staining (a)white stain, and ('b) brown stain. The brown stain is particularlysevere when, as in modern practice, the cold rolled sheet or strip iscoiled into tightly wound coils which are annealed in this form.

White stain is produced by a surface etching of the aluminium by freeacids which might be present in the form of acid additives or whichmight be produced by the decomposition of originally neutral additives,such as lanolin or other esters.

It is already known that the load-bearing capacity of alubricant whichdetermines the percentage reduction in thickness which can be achievedduring the cold rolling of a sheet of metal without the surface damagewhich results from the breakdown of the lubricant, is dependent on thechain length of the molecule of the load-bearing "additive and on itspolarity.

It follows that the longer the chain length of the additive, the betterits load-bearing capacity. It is found, however, that the greater thechain length of the additive used in cold rolling aluminium, the greateris the tendency for the aluminium to form brown stains, which mar thesurface appearance of the rolled sheet on subsequent annealing. Thesebrown stains can be removed by annealing the sheet at a highertemperature and for a lo'nger time than are required by strictlymetallurgical requirements for softening the sheet after cold rolling.

Where the sheet produced with the aid of known lubricants has to beannealed at a relatively low temperature, as for example in theproduction of a part-hard sheet from fully hardened cold rolled sheet,it is impossible to remove the brown stains and the only way to obviatethem is to remove the lubricant from the surface of the sheet beforeannealing is commenced.

It will be appreciated that the removal of the brown stains by prolongedheating or avoidance by removal of the lubricant are both expensive andwasteful procedures.

It is an object of the present invention to provide a method for colddeformation of aluminium employing a lubricant, which on subsequentannealing of the aluminium, does not form white stains and which has are duced tendency to form brown stains as compared with atent O2,962,401 Patented Nov. 29, 1960 a lubricant containing an acid or esteradditive of the same load-bearing capacity.

The object of the present invention is substantially achieved by the useof a lubricant comprising a petroleum fraction base oil having lowstaining properties and a small proportion of a long chain saturatedaliphatic alcohol as the load-bearing additive.

As with known additives the load-bearing capacity of these alcohols andtheir tendency to produce brown stains on the surfaces of the aluminiumon heating to annealing temperature both increase with chain length.

However, with straight chain aliphatic alcohols up to lauryl alcohol andparticularly with nonyl alcohol there is no staining due to the additiveon annealing and, provided a specially refined non-staining base oil isemployed, these alcohols can be used as load-bearing substances in thereduction of sheet for subsequent partial annealing with verysatisfactory results. With nonyl alcohol in such a base oil there is nonecessity to dry off the lubricant prior to low temperature partialannealing and this is a most satisfactory lubricant additive providedthat only moderate reductions are employed. The use of nonyl alcohol asan additive to the lubricant oil does per mitof producing part-hardsheet commercially from fully-hardened cold rolled sheet withoutintermediate removal of the lubricant. This is a result not previouslyobtainable with the known additives.

Where heavy reductions are required in each pass of the rolling mill anoil containing a longer chain alcohol -isemployed,.such aslauryl alcoholorvoctadecyl alcohol. Although .octadecyl alcohol has a definitetendency to produce brown stains on aluminium during annealing, thetemperature and time required to remove these stains is substantiallyless than that required with known additives which have been found,moreover, to have a lower loadbearing capacity than octadecyl alcohol.

Lubricants containing additions of lauryl alcohol, the chain length ofwhich is intermediate between that of nonyl alcohol and octadecylalcohol, have been found to be useful in many applications involving thecold form ing of aluminium products which need to be annealed subsequentto working. Thus, in the production of alusheet material by coldrolling, where moderately heavy reductions are required at each pass ofthe rolling mill, an oil containing about 4% lauryl alcohol has beenused with very satisfactory results, the staining produced on heatingthe cold worked material being insignificant. The use of lubricantscontaining higher concentrations of lauryl alcohol allow heavyreductions to be taken at each pass of the mill. Thus, in practice, alubricant containing 6% of technical grade lauryl alcohol has allowedaluminium sheet, which remained stain-free on annealing, to be coldrolled with a reduction of 64% at each pass of the mill.

Further, a lubricant containing from 2 to 8% of lauryl alcohol has beenfound to have excellent characteristics when used as a lubricant in thepunching out of circles or slugs, for use in impact extrusion ofarticles such as thin walled tubes, from thick aluminium or aluminiumalloy sheet. Thus, a lubricant containing 4% lauryl alcohol has beenfound to have an adequate load-bearing capacity for this purpose and,moreover, to lead to a marked reduction in the brown staining which hasbeen found to occur during the annealing of the slugs when these havebeen produced using known lubricants.

In its broadest terms the present invention comprises a method of colddeforming aluminium (including its alloys), characterised in that thelubricant employed between the aluminium and the rolls or deforming toolcomprises a hydrocarbon base oil with a low inherent tendency to stainthe surface of aluminium when heated in contact therewith and containinga small proportion of a saturated aliphatic alcohol having at leastseven carbon atoms. Below heptyl alcohol the load-bearing capacity ofthe alcohol additive becomes rather low and the flash point of thealcohol drops to a point "which may be unacceptable from the point ofvi'ew-of fire hazard. At the other end of the scale alcohols having morethan twenty carbon atoms decrease in solubility in the base oil'so thatit is impossible to maintain sufficient quantities of the additive insolution. With certain special rollings, however, it may be desirable toemploy an alcohol containing more than 20 carbon atoms. In such case themixture of alcohol and base oil is first heated to get the alcoholintosolution. 011 cooling, the alcohol separates out and forms very fineparticles which remain suspended in the base 'oil for-considerableperiods. If the lubricant is used in this condition, it has exceptionalloadbearing capacity and very high reductions can be 'obtained in coldrolling, using such a lubricant.

For operation with a modern high speed mill having continuous floodlubrication in which for economic reasons it is desirable to be able toobtain the maximum possible reduction, a long chain alcohol such asoctatlecyl alcohol is employed as the additive, in a base oil inquantities of about 1-4%, the oil preferably being maintained at atemperature sufiicient to hold the alcohol in solution. The base oilused must be one which has a low tendency to form brown stains, butseveral such oils are commercially available at the present time.A-s'r'nall proportion (about 0.1%) of a surface wetting agent ispreferably added to the base oil to ensure the spread of the lubricantover the entire surface of the metal.

In apractical rolling test on commercial purity aluminium alloyed withl%% manganese, it was found that the maximum reduction obtainable in onepass 'with known lubricants without damage to the surface was 58%. Onreduction beyond this figure, the surface of thealuminiu'm becamedamaged by reason of collapse of the lubricant film, bringing thealuminium into direct contact with the surface of the roll.

On the other hand; on carrying out a rolling test on tlie' same metalwith a lubricant comprising a commercial base oil with 1.8% octadecylalcohol and a small proportion of wetting agent, it was found possibleto obtain a reduction of 63% on one pass. It is possible that thisfigure could have been exceeded, but the power available '-at therolling mill was insufiicient to permit a greater reduction to beobtained.

In tests designed to ascertain the tendency of lubricants to producebrown stains on annealing, which tests comprise the annealing understandard conditions of stacks of sheets cut from cold rolled aluminiumstrip, some of which were coated with lubricants containing what werepreviously believed to be the most suitable load-bearing additives, andsome of which were coated with the lubricant containing as aload-bearing additive 1.8% octadecyl alcohol, only the sheets coatedwith this latter lubricant were found to be free from staining afterannealing the sheets.

In the place of octadecyl alcohol, about 2% of cetyl alcohol can beemployed as the additive where a slightly lower percentage reduction ineach pass is acceptable. Mixtures of long chain saturated aliphaticalcohols, such as cetyl and octadecyl alcohols, may be employed asadditives. Such mixtures can be obtained commercially more cheaply thanthe pure alcohols and give results very little inferior to the use of apure alcohol alone.

Again it is found that a straight chain alcohol has better load-bearingcharacteristics than a branched chain alcohol of thesame number ofcarbon atoms, but economics may make it desirable to employ the lessefiicient branched chain alcohol as the lubricant additive. Alcoholscontaining unsaturated groups are not satisfactory for the presentpurpose.

The improved load-bearing capacity of lubricants containing octadecylalcohol enables greater rolling speeds to be achieved than are possiblewith known lubricants,

so giving economies in time and in power consumption.

Moreover, in some marginal cases, the use of the improved lubricants hasmade it possible to eliminate one pass in a rolling programme, so thatwhere three passes were required to produce 'a given reduction in thethickness of the metal using known lubricants, the use of a lubricantcontaining octadecyl alcohol allowed the same reduction to be achievedin only two passes of the mill.

In such instances the new 'method results in considerable economies inrolling costs.

In ordinary cold rolling-of aluminum strip the cost of the base oil ofthe lubricant used is a factor which has to be taken into account, sothat it is necessary to employ a petroleum fraction which does notrequire very special refining techniques for its production. Thus, anoil which is suitable as a base for octadecyl alcohol or lauryl alcoholfor compounding -a lubricant to use in rolling aluminum strip which issubsequently fully 'annealed,-may itself have a low staining tendencyand still be fully satisfactory for its purpose.

Such oils may be obtained commercially at satisfactory prices and an oilhaving the following properties is suitable=for the purpose:

Boiling"r'ange 250-350 C. (preferably 260420 0.)

Bromine number 0.4 maximum.

Sulfur content 0.08% maximum mum) Acidity: H J

Fresh sample'neutrali's'ed by 0.02 Sample aged for 24 hours at C.neutralised by 0.025 'nigm. 'KOHl'gm.

The lighter and less viscous the oilis, the better it will be. However,against this the fire hazard must beset. Ordinarily a flash point of C.is the minimum for ordinary acceptability, but where special precautionscan readily be taken, an oil of lower :flash point will give goodresults.

Three commercially available base oils found very suitable for thepresent purpose are Mineral Colza, Fusus A and Kerosine 2675 6, whichhave the following properties:

(preferably 0.06% 2;

Fusus A Mineral Keroslne Colza 26756 Bci'i'tg range C 255-350 255-341288-331 'lotal sulfur content ..p c-rcet 1t. 0. 08 0.075 0.08 Bromi'enumben; v V v 0.; I 0 37 H Viscosity in centstdkes at 20 0 7. 38 6. 4068. 139

Farce .taig'e carbon atoms 'rtng structure per(ent-. V 30 32 27Percentage carbon atoms in 'aro-' matie structure "percent" '4 L 8 4.8

Percentage carbon atoms in napht'teaic structure percent- 26. 27 22. 5

These base-oils have themselves some tendency to produce brown stains,but these are removed under the standard annealing conditions foroctadecyl alcohol and lauryl alcohol and substantially stain-free'anneaIed sheet can beproduced.

In finishrollingwhere'surface'appearance of "the product is of primaryimportance, his usual to employ moderate reductions, and in such casesthe load-bearing capacity of the lubricant is not of primary-importance,whilst the tendency of the lubricant-'to-form 'stains is of greatimportance. --1n finish rolling it is therefore preferred to use arelatively'short "chain alcohol, such as nonyl alcohol, which itself hassubstantially no tendency to form white or brown stains when heated incontact with alu- -minium.

Again in cold rolling aluminum sheet to full hardness and subsequentlydrawing it back to partial hardness by low temperature partial annealingat temperatures of ISO-260 C., nonyl alcohol in amounts of l-5% is againthe preferred additive for the lubricant applied to the metal duringrolling, although lauryl alcohol has been successfully tested for thesame purpose and other alcohols containing more than nine and less thantwelve carbon atoms are also suitable. Because of the staining producedby known additives, it is the present practice to absorb the lubricantfrom the sheet by wrapping the rolled sheet in tissue paper beforeannealing. By using a lubricant containing nonyl alcohol as theload-bearing additive during the rolling step, this costly practice canbe avoided, and the coiled strip or sheet can be annealed whilst stillhaving a lubricant film coating its surface.

Although nonyl alcohol itself has practically no tendency to formstains, the commercially available light petroleum fraction base oils,used for the compounding of rolling lubricants, have some tendency toform brown stains, although this is slight compared with thecommercially available additives. When using nonyl alcohol, therefore,as the load-bearing component of the rolling lubricant to secure thebest results, it is necessary to employ a specially refined base oilwhich is itself practically non-staining. Such base oils are notcommercially available and are therefore expensive and can only be usedwhere their use results in other economies.

The characteristics of a suitable base oil for this purpose are:

Bromine number less than 0.2, preferably less than 0.1.

Total sulfur less than 0.02%, preferably less than 0.01%.

Acidity after ageing for 24 hours at 110 C. neutralised by less than0.01 mgm. KOH/gm.

Colour water white.

The fraction should be very close out with only of the oil distillingover outside a narrow boiling range of 20 C. In order to keep anacceptably high flash point of the order of 250 C., the boiling range ofthe base oil should be 275295 C., with only 5% of the sample distillingover at temperatures below 275 C. and a further 5% at temperature above295 C.

Using a base oil of these characteristics nonyl alcohol is added in therange 1 to 5%, preferably with the addition of about 0.1% of a wettingagent to form a lubricant for use in the cold working of sheet, which isto be subsequently partially annealed at a temperature of between 180 to260 C. The amount of nonyl alcohol which is added will depend on thereduction to be etfected, but for ordinary service about 2% nonylalcohol is employed.

Additions of laryl alcohol have been used with success in the rolling ofvery thin aluminium sheet or foil to produce a very high surface finish.It is usual in the production of such foil to employ a light petroleumfraction to which is added up to about 12% of various esters and fattyacids, including palm oil and coconut oil, and special treatments arerequired to minimise the staining produced when these lubricantsdecompose during annealing. It has been found that virtually stain freefoil, having the desired high surface finish, can be produced by coldrolling the foil stock with a lubricant comprising a light petroleumfraction to which is added 3% of lauryl alco- 1101. However, for theproduction of foil having an exceptionally high finish, it is necessaryto use a lubricant containing as the main load-bearing additive 24%,preferably 3%, of lauryl alcohol, to which is added 1 to 2% of palm oil.Using this lubricant virtually stain free foil, having an exceptionallyhigh finish, can be produced without the necessity of employing specialannealing treatments, involving times and temperatures in excess ofthose required to anneal the metal.

I claim:

1. In a process for the cold deformation of aluminum, the step oflubricating the surface of the aluminum with a composition consistingessentially of: (a) a hydrocarbon oil having not more than a slighttendency to produce stains on aluminum when heated in contact therewith,(b) an amount sufiicient to improve the load-bearing capacity of saidhydrocarbon oil of at least one saturated aliphatic alcohol having atleast 7 carbon atoms, (0) from zero to an amount at least sufiicient toensure the spread of the lubricant over the entire surface of the metalto be deformed of a surface-wetting agent, and from zero to about 2%palm oil.

2. The process of claim 1, in which said aliphatic alcohol is a straightchain alcohol having 9 to 20 carbon atoms; and in which the amount ofsaid alcohol used is from about 1% to about 8% by weight of saidcomposition.

3. The process of claim 1, in which said aliphatic alcohol is laurylalcohol, and in which this alcohol is present in an amount from about 2%to about 8% by weight of the entire composition.

4. The process of claim 1, in which said aliphatic alcohol is octadecylalcohol, and in which this alcohol is present in an amount from about 1%to about 4% by weight of the entire composition.

5. A process for cold rolling aluminium foil stock to produce a foilhaving a high surface finish, characterised in that the foil stock islubricated during rolling with a composition consisting essentially of alight petroleum fraction oil of low tendency to form brown stains onaluminium when heated in contact therewith, about 24% lauryl alcohol,and about 12% palm oil.

6. A process for the production of part-hard aluminum sheet material,comprising cold rolling aluminum, whilst lubricating it with acomposition consisting essentially of (a) a close-cut hydrocarbon oilhaving substantial freedom from formation of brown stains when heated incontact with aluminum, (1)) an amount suflicient to improve theload-bearing capacity of said hydrocarbon oil of a straight chainaliphatic alcohol containing 9 to 12 carbon atoms as a load-bearingadditive, and (c) from zero to an amount sufiicient to ensure the spreadof the lubricant over the entire surface of the metal to be deformed ofa surface-wetting agent; and subsequently annealing the rolled aluminumat a temperature in the range of about to 260 C. to draw it back topart-hardness.

References Cited in the file of this patent UNITED STATES PATENTS1,841,070 Story Jan. 12, 1932 2,119,114 Richardson et al. May 31, 19382,409,726 Winning et a1 Oct. 22, 1946 2,590,451 Perry Mar. 25, 19522,605,224 Jahn July 29, 1952

1. IN A PROCESS FOR THE COLD DEFORMATION OF ALUMINUM, THE STEP OFLUBRICATING THE SURFACE OF THE ALUMINUM WITH A COMPOSITION CONSISTINGESSENTIALLY OF: (A) A HYDROCARBON OIL HAVING NOT MORE THAN A SLIGHTTENDENCY TO PRODUCE STAINS ON ALUMINUM WHEN WHEN HEATED IN CONTACTTHEREWITH, (B) AN AMOUNT SUFFICIENT TO IMPROVE THE LOAD-BEARING CAPACITYOF SAID HYDROCARBON OIL OF AT LEAST ONE SATURATED ALIPHATIC ALCOHOLHAVING AT LEAST 7 CARBON ATOMS, (C) FROM ZERO TO AN AOMOUNT AT LEASTSUFFICIENT TO ENSURE THE SPREAD OF THE LUBRICANT OVER THE ENTIRE SURFACEOF THE METAL TO BE DEFORMED OF A SURFACE-WETTING AGENT, AND FROM ZERO TOABOUT 2% PALM OIL.
 6. A PROCESS FOR THE PRODUCTION OF PART-HARD ALUMINUMSHEET MATERIAL, COMPRISING COLD ROLLING ALUMINUM, WHILST LUBRICATING ITWITH A COMPOSITION CONSISTING ESSENTIALLY OF (A) A CLOSE-CUT HYDROCARBONOIL HAVING SUBSTANTIAL FREEDOM FROM FORMATION OF BROWN STAINS WHENHEATED IN CONTACT WITH ALUMINUM, (B) AN AMOUNT SUFFICIENT TO IMPROVE THELOAD-BEARING CAPACITY OF SAID HYDROCARBON OIL OF A STRAIGHT CHAINALIPHATIC ALCOHOL CONTAINING 9 TO 12 CARBON ATOMS AS A LOAD-BEARINGADDITIVE, AND (C) FRO ZERO TO AN AMOUNT SUFFICIENT TO ENSURE THE SPREADOF THE LUBRICANT OVER THE ENTIRE SURFACE OF THE METAL TO BE DEFORMED OFA SURFACE-WETTING AGENT, AND SUBSEQUENTLY ANNEALING THE ROLLED ALUMINUMAT A TEMPERATUER IN THE RANGE OF ABOUT 180* TO 260*C. TO DRAW IT BACK TOPART-HARDNESS.